They both need visas, but since Arshavin is a first team National Team, it should not be a problem to get one. As for Dudu, he is brazilian, and also needs a visa. He was a regular in the National team last year. I read somewhere that if he was to come to the EPL and there is an issue with his visa, Dunga would help out by writting a letter.
Having them both at Everton, would be amazing!